Nongrounded or metallic circuit system



March 31, 1925. 1,531,494

E. A. MELLINGER NONGROUNDED OR METALLIC CIRCUIT SYSTEM Filed April 18,1907 2 Sheets-S116 1 CPQK/W 6 a WWW. Affwwa??? March 31, 1925,

E. A. MELLINGER NomouNDED on QE'rALLIc CIRCUIT SYSTEM Filed April 18.1907 2 Sheets-Sheet 2 Patented Mar. 31, 1925.

UNITED STATES PATENT OFFICE.

EDWARD A. HELLINGm OF CHICAGO, ILLINOIS, ASSIGNOR, BY MERE ASSIGNMENTS,TO AUTOMATIQ ELECTRIC COMPANY, A CORPORATION OF ILLINOIS.

' HONGBOUNDED OR METALLIC CIRCUIT SYSTEM.

Application filed April 18, 1507. Serial No. 889,012.

Metallic Circuit Systems, of w iich the following is a specification.

My invention relates to telephone systems in eneral, but more particuarly to automatlc or semi-automatic telephone exchange systems, andespecially to systems in whichno operating grounds are employed at thesubscribers substations. Prior to my 1nvention it was proposed tooperate switches without employing the ground or earth between thesubstations and the exchange, for.

both connecting and releasing purposes. In my improved system, however,as herein disclosed, new and improved means are provided by which aseries of switches can be successively operated or controlled from asubstation at which no ound connection is provided, whereby the inecircuits for controlling the switches all include the two sides of theline in series. Furthermore, with my improved arrangement means areprovided by which the calling subscriber can release the diiferentswitches by which a connection was extended to the called subscribersline-that is to say, by simply opening the line circuit, when he hangsup his receiver, the calling subscriber may release the switches at anystage of the call, either before or after the called subscribe ranswers. In addition, the subscribers individual switches are of suchcharacter that they cannot remain ofi normal-that is to say, theseswitches cannot be retained in an operated position unless theirrespective telephone lines are closed at the substations. In this waythe trouble and annoyance which usually results from off-normal switchesis avoided, as an accidental ground on any telephone line will not causethe individual switch thereof to operate, the operation of the switchbeing dependent upon the closing together of the two sides of the line.With this arrangementI provide improved means for trunking on apercentage basis, and make it possible to automatically trunk a callingtelephone line into connection with a called telephone line in aten-thousand or even larger exchange, without the necessity of employingoperating grounds at the substations. As stated, the mere act on thepart of a subscriber in hanging up his receiver is sufiicient toimmediately release and restore any trunkin connection which may havebeen establis ed between his line and the line of some other subscriber.Such act, as will hereinafter more fully appear, is also sufiicient torelease any switch or switches which may have been 0 rated by thecalling subscriber, should he or any reason decide to hang up hisreceiver before the connection has been fully extended to the line ofthe called subscriber. These and other advantages will hereinafter morefully appear.

In the accompanying drawings, Figures 1 and-2 taken together re resentdiagrammatically a calling substation A connected, by means of centralofiice switching apparatus, with a called substation A, in a systemembodying the principles of my invent-ion. The switches through whichthe stations A and A are shown connected comprise (in Fig. 1) theso-called first-selector C which is allotted to the calling line, andthe second-selector D, and (in Fig. 2) a connector E and afirst-selector C of the called line. The selector C is individual to thelin of the substation A, while the first-selector C is individual to theline of the substation A. The said selectors C and O are alike. Foroperating the central oflice switches there. is provided a centralsource of current or battery B having its positive terminal preferablygrounded at G (Fig. 2). It will be understood, of course, that in thissystem the first-selectors are arranged in groups, as well as thesecond-selectors and connectors. A somewhat common arrangement is todivide the subscribers and their allotted first-selectors into groups ofthousands. Each thousand-group is sub-divided into groups ofone-hundred. Then the like hundreds-that is, the one-hundreds,thetwohundreds, etc.-of the various thousands are each arranged in onegroup, so that in a tenthousand system the one-hundreds of the thousandsform one group, the two-hundreds a second group, etc. Furthermore, eachbank level of each of these hundred-groups has allotted to it one groupof second-selectors allotted to the thousand corresponding to thelevelthat is, the second-selectorgroup of the first-selector first banklevel is allotted to the first thousand, the second level to the secondthousand, etc., thus takof the hundreds; there being in a tenthousandsystem ten one-thousand-groups of first-selectors; tenone-hundred-groups in each thousand; also ten groups of secondselectors,one for each t ousand and ten ement groups'of connectors in eachthousand, one

or each hundred. With this arrang it will be understood that thefirstlevel of the first hundreds in all thousands in the system is multipliedin a manner well understood likewise the second level, etc. Also,

all like levels of each second-selector-grou one of which, as stated, isalloted to eac -t ousand) are likewise multiplied. In each of theaforesaid connector-groups, and in the same manner, the like levels are,of

course, also multiplied. In this way the individual switches are thesame in number as the subscribers, but all other switches are 28 g Itwill be clear from the drawings that when employed on a percentagebasis.

The substations in the system ma be of any suitable or approved type. esubstation A, for example, comprises a receiver 2, a'switch-hook 3 forcontrolling the substation circuits, which controlling o erations areaccomplished through the me ium of any suitable means, such as thecam-arms 4 and 5. When the switch-hook is down the cam-arm 4 holds thespring 6 out of engagement with the spring 8 and in enga ement with thespring 7, thereby bridging t e ringer 9 in series with the condensers 10and 10 across the line. When the switchhook descends the said camdisengages the springs 11 and 12, thus breakin the local circuit whichincludes in series t e primary winding 13, transmitter 14 and localbattery 15. The said substation comprises the usual induction-coil 16having the primary winding 13 and secondary winding 17. Being anautomatic substation it is provided with impulse springs. The springs18- and 26 are the vertical impulse springs and the springs 19 and 30are the rotary impulse springs. Said substation is, of course, providedwlth -a dial (not shown) which is secured tothe shaft 20, together withthe locking do 21. This dial is ordinarily located on the ack side ofthe im ulse wheel 23, as also the switch-hook 3, ut for convenience ofillustration this .is shown diagrammatically. Furthermore, there is alocking cam 22 that locks the dog 21, while the receiver is on theswitch-hook, to prevent rotation of the impulse teeth 24 an .to Keith,Erickson & Erickson.

dial. Foro ra' theim ulse rin 1s and 26 and l the sl fbstati dh ismosecured to the shaft 20, which lse'wheel carries on its periphe theso-ca ed vertical one rotary impulse 'vided with an impulse wheel 23that is tooth 25. The said im ulse teeth are so arranged that when the'al is drawn down the im ulse springs are notopera'ted; but as the ialreturns, first thevertical impulse teeth operate to close the verticalimpulse s rings 18- and 26, and after they have come p ete their workthe rotary impulse teeth 25 operates to separate the rotary impulsesprings 19 and 30. In this operation the vertical impulse spring 18 ispressed'into contact with the spring 26 a number of times, whereby thevert cal line conductor 27 becomes directly connected with the rotaryline conductor 28. Normally, when the receiver is removed, the verticaland rotary line conductors27 and 28 are connected through the highresistance coil 29. After the vertical impulse teeth have operated thevertical impulse springs, the rotary impulse tooth 25 momentarilydisengages the springs 19 and 30, whereby the line conductors 27 and 28become separated, and when the v springs engage, the line conductors 27and "are again connected through the coil 29.

the subscriber pulls down the dial the rotary impulse tooth 25, uponrotating in a forward direction, meets the angled member shown on theend of the spring '19, pressing as it advances, both s rin 19 and 30 outof the way, but without rea ing connection. However, when the dialreturns toward normal position the impulse tooth 25 comes in behind themember on the. end of the sprin 19, flexing the'said -s ring 19 awayfrom t e spering 30, thus brea 'ng the circuit, as descri d. It will beunderstood, furthermore, that the shaft 20 is provided with a propertension sprin adapted to restore the dial when once it as beenrotatedout of normal position. Furthermore, the switch-hook 3 is also providedwith a suitable spring whereby said switch-hook may be caused to risewhen theweight' of the receiver is removed. Means wh reby the subscribermay si nal the called ubscriber comprises the pus ,-button 31 which,when pressedfcarries the spring 32 into engage- The first-selector maybe of any suitable- I or approved type, for instance of the general typedescribed in United States Letters Patent No. 815,321, granted March 13,1906,

The firstselector 0 herein shown, however, is characterized by a numberof new features. It embodies the following details and circuits: aswitch shaft 34 that carries the vertical and rotary wipers 35 and 36,respectively, and the private wiper 37, and aside switch which is wellknown and which comprises the side switch wipers 38, 40, 41 and 42. Theside switch is under the control of the private magnet 43, and when theside switch is in normal or first position the wipers 38, 40, 41 and 42occupy the contact points 44, 46, 47 and 48, respectively. In the secondposition they rest on the contact points 49, 51, 52 and 53,respectively, and in the third position the contact points 54, 56, 57and 58 are engaged by their respective wipers. Through the medium of thevertical line relay 59, and while the side switch is in first position,the subscriber controls the vertical magnet 60, which latter operates toraise the switch shaft 34 and wipers 35, 36 and 37 vertically. By meansof the rotary line relay 61, and after the switch shaft has been raisedto close the springs 62 and 63but before the shaft has rotated todisengage said springs-the subscriber controls the private magnet 43and, therefore, the side switch. While the side switch is in secondposition the rotary magnet 64, which operates to carry the switch shaftand wipers 35, 36 and 37 in a rotary direction, is energized. Associatedwith this rotary magnet and in series therewith there is, as usual, acircuit interrupter, the springs of which are shown at 141. Thisinterrupter may be of any design, but the interrupter disclosed inUnited States Letters Patent No. 841,004, granted January 8, 1907, toJohn Erickson, for improvement in interrupter for electro-magnets,discloses one form that is especially adapted to operate with the switchC, or with any other selector disclosed in this system. The relay 65provides the means whereby the subscriber controls the release magnet66. The release magnet and mechanism is of the character shown inconnection with the release magnet of the connector disclosed in UnitedStates Letters Patent No. 815,176, granted March 13, 1906, to Keith,Erickson & Erickson-that is, when the release magnet 66 is energized itsarmature is at-.

tracted, and the release and restoration of the switch shaft and sideswitch is brought about immediately, even before the release magnetde-energizes, in the same manner in which the connector is released inthe said patent. The bridge-cut-olf relay 68 is provided to open theconnection between the line relays 59 and 61 and the battery terminals.It 'will be seen that the vertical line relay 59 is connected to thenon-grounded terminal, and that the rotary line relay 61 is connected toground. This disconnection is for the purpose of preventing the linerelays 59 and 61 from chattering when ringing current for signaling thesubscriber A is sent over the line. It is also desirable to remove thebridge formed through the said relays from across the line to give thevoicecurrents as clear a path as possible. Furthermore, the shaft 34 isprovided with the cam 69 which, when'the shaft is in normal position,permits the "springs 62 and 63 to disengage; but on the first verticalstep of the shaft 34 the cam 69 presses the said springs intoengagement. Now, when the shaft is given a rotary step the cam 69 iscarried out of engagement with the spring (53, and the springs 62 and 63disengage. The switch shaft is provided with a normal arm 70 which, whenthe shaft is given a vertical impulse, permits the spring 71, whichnormally engages the spring 72, to pass into contact with the spring 73,and then to carry this latter spring into contact with the spring 74.

The second-selector D is similar to the first-selector C, with theexception that there are no normalconductors such as the normalconductors. and 70. Since there is no1 use for such conductors they areomittet. ond-selector for a bridge-cutoff relay such as the relay 68of'the selector C, and it is also omitted, and the line relays areconnected directly to the battery terminals. The private normalconductor, such as the private normal conductori77 of the selector C, isof no use in connection with the second-selector and is also omitted.This selector is, however, equipped with the verti cal magnet 78 and therotary magnet 79, the release magnet 80 and the private magnet 8 1. Thesaid private magnet 81, of course, controls the side switch wipers 82,83, 84 and 85. The vertical movement of the switch shaft 86'and,therefore, of the wipers 87, 88 and 89 is controlled by the verticalmagnet 78, and the rotary movement by the rotary magnet 79. the rotarymagnet circuit being provided with the usual interrupter springs 90. Theoperative magnets of the switch are, of course, controlled by thesubscriber through the use of the vertical and rotary line relays 91 and92, as is well known. Said relays have under their control the usualsprings 93, 94 and 95. The selector D is also provided with a releaserelay 96 for controlling the release of the switch. The release magnet80 and mechanism is of the type described in said connector patentthatis, when the release magnet is energized and the armature attracted, theswitch shaft and side switch are restored to normal position. It will beunderstood that in both the selectors C and D the release magnetmechanism is of the type employed in the connector switch instead ofthat usually employed in selector switches of the general type disclosedin said selector patent. The cam springs 97 and 98 are controlled byThere is also no necessity in the sec- 3;

ion

- known, are very much the same. The connector switch shaft 104, likethefirst-selector switch shaft, carries the line wipers 105 and 106 and theprivate wiper 107. The connector switch is also controlled by thecalling subscriber through the medium of the vertical and rotary linerelays 108 and 109. The vertical line relay directly controls theverticalmagnetllO, and also the rotary magnet 111 and the ringer relay112. The ofiice of the vertical magnet 110 is to give the shaft andshaft wipers their vertical motion, and the rotary magnet 111 imparts tothe shaft and shaft wipers a rotary or circular motion. The rotary linerelay 109 controls the energizing circuit-of the release relay 113. Therelease relay 113 is similar to the relay 96 of the second-selector andthe relay of the first-selector. The private magnet 114 is controlled bythe rotary line relay 109, and under certain conditions controlstherelease magnet 120 and also the side switch wipers 115, 116, 117, 118and 119. j The side switch of the connector, like the side switch of thefirst-selector, has a normal or first position, a second position and athird nsition. By the condensers 122 and 123 the talking circuit throughthe connector is divided into two inductively-connected sections. Thecentral office is equipped with a busy-signaling apparatus of anysuitable design, as, for example, the one comprising an interru ter H inseries with the primary windmg 121 of the induction-coil 124, whereby abusy-signaling current is induced in the secondary winding 125 of thesaid coil. The connector switch shaft 104 also carries a normal post arm126 which, when the connector shaft is oil normal, allows the spring 127to engage the contact point 128, whereby the busy-signal may betransmitted to the rotary line conductor. Also, when the shaft is givena vertical step the springs 129 and 130 engage, whereby the releasemagnet 120 is connected to the battery lead. 1 V a The substation A islike the substation A; also, the first-selector switch 0' allotted tothe line #2220 is like the first-selector switch C allotted to the line#5000.

A clearer understanding of my improved system may be had b following theoperation of the centralo ce switches when one subscriber calls another.Suppose, for an example, that the subscriber at substation A desires tocommunicate with thesubscriber at substation A on the line #2220. Theoperation of the central oflice switches to bring about this connectionis as follows: When the subscriber at substation A removes the receiver2 from the switch-hook 3 the cam-arm 4 permits the springs 6 and 8 toengage, whereby a series circuit including the vertical line relay 59 ofthe selector resistance coil 29 of the substation A and the rotary linerelay .61 of the selector G, is closed. This circuit extends from groundG at the selector 0 through the springs 131 and 132, throu h therotary'line relay 61, rotary line COINfilCtOI 28, through the sprin 30and 19, springs 6 and 8, secondary win .ing 17, receiver 2, through theresistance coil- 29 to the vertical line conductor 27, side switch wiper38, vertical line relay 59, springs 133 and 134 to the battery lead 135,thence through battery Band to ground G. The rotary l1ne relay 61 is soarranged that the current-flow is sufiicient to operatively energize thesaid relay, while the vertical line relay 59 is so arranged that thecurrentflow in this circuit is not sufficient to operatively energizeit. The rotary line relay, upon energizing, laces the springs 136 and137 in contact. is closes a circuit through the release controllingrelay 65. The circuit through the release controlling relay extends fromground G. through the springs 136 and 137, throughthe relay 65 to thebattery lead 135, thence through battery and to ground G. This relay,upon ener izing, separates the springs 138 and 139, w ich disconnectsthe battery lead 135 from the releasemagnet 66. When the dial is rotatedfor the first digit 2 the spring 18 is twice pressed into contact withthe s ring 26. By this operation the line con uctors 27 and 28 aredirectly connected, shunting or short-circuiting' the resistance coil29; thus a new circuit w ich does not include the resistance coil 29 isestablished through the vertical and rotaig line relays 59 and 61 of theselector C. uflicient current now flows in the cir cuit to operativelyenergize the vertical line relay 59, which latter, upon energizing,presses the springs 140 and 136 into contact, which closes anenergizing. circuit through the vertical magnet 60. This circuit extendsfrom ground G through the springs 136 and 140, through the verticalmagnet 60 to the battery lead 135, thence through batter B and to groundG. The springs 18 an 26 being pressed into contact twice for the firstdigit, the vertical line relay 59 is operatively energized twice, and inturn the vertical, magnet is energized and operated twice. By thisoperation of the vertical magnet the shaft 34 and the shaft wipers 35,36 and 37 are raised two steps and brought opposite the second banklevel. It should be borne in mind that at the first vertical step of theswitch shaft the cam 69 o eratcs to close thenornially open shaftsprings 62 and 63 in contact. As soon as the said springs 62 and 63 comeinto contact an energizing circuit is established through the privatemagnet 43 from ground G at the selector C, through the springs 136 and137, through the cam springs 62 and 63 to the private magnet 43, thencethrough said magnet to the battery lead 135, and through battery B toground G. Furthermore, at the same first vertical ste the normal postarm70 disengages from t e spring 71, permitting the latter to leave thespring 72 and to engage the spring 73, and to carry the said 5 ring 73into enga ement with the groun ed spring 74, where y the springs 71, 73and 74 are maintained in contact while the shaft is off normal. Thisoperation disconnects the privan-v normal conductor 77 from thebridge-cut-oif relay 68, and places a guarding potential on said privatenormal conductor from ground G to prevent any calling subscriber fromcalling-in upon the line #5000 after the switch C has been operated.When the rotary impulse tooth 25 operates to separate the springs 19 and30, and to thus open the line, the circuit including the vertical androtary line relays and resistance coil 29 is broken. line relay 61 is,therefore, deprived of its energizing current and de-energizes,permitting the springs 136 and 137 to separate,

whereby in turn the energizing circuit of the private magnet 43 isbroken and the side switch is permitted to pass to second position. ItWlll be understood that when the vertical impulse teeth 24 close thecircuit between the springs 18 and 26, the vertical line relay 59remains operatively energized only as long as the said springs aremaintained in contact. As soon as the impulse tooth 25 disengages fromthe spring 19 the springs 19 and 30 again come into contact, and againthe energizing circuit through the rotary line relay is established.Although, in the meantime, the circuit through the release controllingrelay is broken,'said rela being slow-acting retains suifici'ent residuamagnetism to maintain its armature in an operated position until thisenergizing circuit is again established, when the rotary line relayenergizes. When the side switch passes to second position an energizingcircuit is established through the rotary magnet '64. This circuitextends from the grounded contact point 53 through the side switch wiper42, interrupter springs 141, rotary magnet 64 to the battery lead 135,thence through battery B to ground G. The rotary magnet, uponenergizing, oper- The rotary ates to carry the shaft wipers in a rotaryor circular direction. The rotaryv magnet being ener ized one step, theshaft wipers 35, 36 and 3 are carried into engagement with the first setof bank contacts, which contacts, it is assumed, constitute theterminals of the trunk line leading to the selector switch 1); but ifthe first trunk line is busy some other selector (similar to theselector C) in the exchange will be resting in engagement with saidtrunk line, and the first private bank contact of the second level willbe found connected to ground, as is the case in systems of this generalcharacter. Therefore, when the selector shaft is rotated one step anenergizing circuit is established through the private magnet 43 when theprivate wiper 37 strikes the grounded rivate bank contact, therebyretaining the side switch in second position and maintaining anenergizing clrcuit through the rotary magnet 64. The rotary magnet, byintermittent energization, causes the shaft. to rotate step by step andcarry the wipers past the last busy trunk line. However, as soon as theprivate magnet is de-energized the side switch is tripped into thirdposition; but if there are no busy contacts to be passed over, asassumed in the first instance, the rotary magnet 64, as is well known,trips the side switch to third position, with the result that the sideswitch Wipers engage their respective contact points in third position.When the side switch wipers 38 and 40. pass to third position thesubscribers line conductors 27 and 28 are extended to the conductorleading to the selector switch D. Also, since the side switch wiper 41engages a grounded contact oint 57 a guarding potential is -establisheat the private wiper 37 for protecting the seized trunk line from beingmolested or disturbed by any other switch. It will be seen thatwhen theshaft is given the first rotary step the cam 69 passes out of engagementwith the spring 63 and permits the springs 62 and 63 to disengage. Thisdisengagement breaks the energizing circuit formed by the rotary linerelay 61 through the private magnet 43. The private magnet 1s, however,still subject to the control of the private wiper 37, when the sideswitch wiper 41 is in second position, as already described. It willalso be seen that the selectors are of the bridging type, inasmuch asthe vertical and rotary line relays are permanently connected to theline conductors. As a result of this construction, the energizingcircuit through the rotary line relay 61 is maintained and,consequently, the energizingcircuit of the release relay 65. The seconddi it is called after the subscriber has establlshed connection with theselector D by way of the trunk conductors 142 and 143. When the trunkconductors 142 and 143 are seized an, energizing circuit is establishedthrough the vertical and rotary line .relays 91 and 92 of the selectorD, in the 94 and 95, through the relay 96 to the battery lead 135,thence through'battery B to ground G. The relay 96 energizes anddisengages the springs 144 and 145, whereby the release magnet 80 isdisconnected from the battery lead. The subscriber then rotates thedial, as described, for the second digit 2, thereby shunting orshort-circulting the resistance coil 29 when the springs 18 and 26engage. The vertical line relay 91 now operatively energizes and placesthe springs 93 and 94 in contact, whereby a C11- cuit is closed throughthe vertical magnet 78,.said circuit extending from ground G through thesprings 94 and 93, through the magnet 78 to the battery lead 135, thencethrough battery B and to ground G. Each time that the vertical magnet 1senerglzed it operates to raise the shaft and shaft wipers one step at atime, unt1l the said wipers are carried two steps and-brought oppositethe level in which are located the terminals of the trunk conductors 144and 145 leading to the connector switch E. In the same manner describedin connection with the selector C, when the switch shaft 86 of theselector D rises for the first step the cam 99 presses the cam springs97 and 98 into contact, whereby an energizlng circuit is set up throughthe private magnet 81. This energizing circuit extends from ground Grthrough the line relay springs 94 and 95, through the cam springs 97 and98 to the private magnet 81, thence to the battery lead 135, and throughbattery B to ground G. When the rotary impulse tooth 25 separates thesprings 19 and 30 the energizing circuit through the rotary line relay92 is interrupted, and the said relay restores the springs 94 and. 95 tonormal position, which breaks the energizing circuit through the privatemagnet 81 and the release relay 96. The private magnet uponde-energizing, permits the side switch to pass from first to secondposition. The release relay 96 being slow-acting, however, does not havetime to fall back. When the side switch wiper 85. engages the groundedcontact point 146 an energizing circuit is established through therotary magment 79.

I This circuit extends from the grounded conbattery B and to ground G.The rotary magnet, by intermittent magnetization, operates to rotate theshaft and shaft wipers step by step and carry the wipers past the lastbusy trunk line, if any such are found, and as described in connectionwith the selector C. 1191141118 wiper 89 disengages from the last busytrunk line the energizing circuit (extending from the grounded pri--vate contact to the private wiper 89, side switch wiper 84, contactpoint 147,-throughthe private magnet 81 to the battery lead 135, thencethrough battery B and to ground G) is broken, and thecside switch passesto third position, thus extending the subscribers line conductors 27and'28to the conductors 144 and 145 which-lead to the connector switchE. Or. if the first trunk is idle, the rotary magnet trips the sideswitch to third position. as already explained. When the side switchpasses to third position the side switch wiper 84 engages the groundedcontact point 148, and a guarding potential is established at theprivate wiper 89 for protecting the seized trunk line from beingmolested by any other switch. In this selector, as in the'selector C,the energizing circuit through the rotary line relay '92 is maintainedeven after the side switch passes to third position; consequently, thecircuit through the release relay 96 remains unlnterrupted. Since thesubscribers line conductors 27 and 28 are new extended to the connectorE. a circuit is established through the vertical line relay 108,,resistance coil 29 at the substation A, rotary line relay 109 of theconnector E. It will be seen that in each instance when the'subscribersvertical and rotary line conductors 27 and-28 are extended to the nextswitch, a new energizing circuit is established through the line relaysof the new'switch in multiple with the line relays of the old swltches,and through the substation reslstance coil 29. The subscribers conductors 27 and'28 having been extended to the connector E, the'rotary linerelay 109 operates and places the springs 149 and 150 in contact. whichcloses a circuit through the releasing relay 113. This circuit ex: tendsfrom ground G through the springs 149 and 150, through the winding'ofthe relay 113 to the battery lead 135, thence through battery B and toground G. The relay 113 now operates to disengage the springs 151 and152. The subscriber then operates the dial for the third digit 2,thereby energizing the vertical line relay 108 twice and de-energizingthe rotary line re-' lay 109 once. The current for energizing thevertical line relay flows from ground G through the rotary line relay109 to the trunk conductor 145. shaft wiper 88, side switch wiper 83,conductor 143, shaft wiper 36, rotary line conductor 28, springs 26 an d18 to the vertical line conductor 27, side switch wiper 38, shaft wiper35, conductor thence to the battery lead .135, and through battery B toground G. Each time that the vertical. line relay is energized the linerelay springs 153 and 149 are pressed into contact, thereby closing anenergizing circuit through the vertical magnet 110. The circuit throughthe vertical magnet extends from ground G through the springs 149 and153, side switch wiper 117, through the vertical magnet110 to thebattery lead 135, thence through battery B and to ground G. Each timethat the vertical magnet is energized it operates to raise the shaft andshaft wipers one step at a time, until the said wipers are carried twosteps and brought opposite the level in which are located the terminalsof the line #2220. When the rotary line relay 109 de-energizes, owing tothe break or rotary impulse, the circuit through the private magnet 114is broken. The private magnet now de-energizes and permits the sideswitch to pass to second position, thus placing the side switch wipers115, 116, 117, 118 and 119 in connection with their respective contactpoints in second position. During the instant at which the rotary linerelay 109 is de-energized, the releasing relay 113 is maintained in itsoperated position by the residual magnetism, in the same manner in whichthe relays and 96 of the selectors C and D are retained in theiroperated position during the rotary impulse. The last digit being naughtthe subscriber energizes the vertical line relay 108 ten times and therotary line relay 109 onoe. However, when the line relay springs 149 and153 engage, a circuit is closed through the rotary magnet 111 instead ofthrough-the vertical mag-' net 110. -This energizing circuit extendsfrom ground G through the springs 149 and 153. side switch wiper 117 tothe rotary magnet 111. thence to the battery lead 135, and throughbattery B to ground G. Each time that the rotary magnet is energizedrupted. The private magnet de-energizes and one of two results occurs,namely the release of the side switch from second to third position, orthe so-called busy-release of the connector, which will be disclosedhereinafter. Suppose the former result to occur and the side switch topass 'to third position, thus placing the side switch wipers 115, 116,117, 118 and 119 in contact with their respective contact points inthird position. Then when the-side switch passes to third position. theside switch wiper 119 engages the third-position contact point, which isgrounded, and as a result a guarding potential is established at theprivate wiper 107 for protecting the called line. This potential extendsfrom ground Gr through the side switch wiper 119 and to the privatewiper 107 which engages the private contact of the called line. Theengagement of the side switch wiper 119 and the third-position contactpoint also closes an energizing circuit through the cut-off relay 157 ofthefirst-selector C, thereby removing the bridge/formed by the rotaryand vertical line relays ,158 and 159 of the selector C across thecalled line. i The energizing circuit for the relay 157 may be tracedfrom ground G to the private wiper 107, thence through the privatenormal conductor 156, switch shaft springs 158" and 159 to thebridge-cut-ofi'relay 157, thence to the battery lead 135, and throughbattery B to ground G. .Of course. when the relay 157 energizes itseparates the springs-160 and 161 from the springs 162 and 163, therebydisconnecting the relays 158 and 159 from the battery terminals.

To signal the called subscriber, the calling subscriber presses thesignaling button 31, whereby the spring 32 is placed in contact with thecontact point 33, as a result placing in direct connection the verticaland rotary line conductors 27 and 28. This now causes an increaseof-current-fiowdhrough the vertical line relay 108 of the connector E.It will be remembered that the connector side switch has passed fromsecond to third position, and that the side switch wiper 117 is inengagement with the contact point 164, thereby placing the verticallinerelav 108 in control of the ringer relay 112, in the same manner inwhich the rotary magnet 111 came under the control of the vertical linerelay 108 when the side switch passed from first to second position.Therefore, when the vertical line relay 108 presses the springs 149 and153 into contact, the ringer relay 112 is energized by a flow of currentfrom ground G through the springs 149 and 153, side switch wiper'117,contact point 164, ringer relay 112 to the batterv lead 135, and throughbattery B to ground G. The ringer relay, upon energizing, shifts thesprings 165 and 166 from the springs 167 and 168 to the springs 169 and170. This results in separating the calling subscribers line from thecalled subscribers line and bridging across the line of the latter, m

the terminals of the ringer generator I. The signaling current is,therefore, sent from the ringer generator I to the ringer generatorsprin s 169 and 165, side switch wiper 115, sha t wiper 105, normalconductor 154, vertical line conductor 171,'condenser 172, rin or 173,condenser 172, s rings 174 and 1 5, rotary impulse springs 176 and 177to the'rotary line conductor 178, normal conductor 155, shaft'wiper 106,side switch wiper 116, ringer relay springs 166 and 170, back to thegenerator I. As soon as the calling subscriber ceases to press thesignaling button 31 the ringer relay 112 becomes de-energized and thesprlngs 165 and 166 resume-their normal position in contact with thesprings 167 and 168. The subscriber A, in response to the signal,removes the receiver 179 from the switch-hook 180, thereby removing theringer 173 from across his line and bridging instead the secondarycircuit which includes the receiver 179, the

' secondarywinding 181 of the induction-coil 182, secondary springs 183and 175, and rotary impulse springs 176 and 177. The 10- cal transmittercircuit is closed as soon as the springs 185 and 186 engage in contact.The two substations #5000 and #2220 are now connected over the circuitshown by heavy lines in Figs. 1 and 2.

The release of the central oflice switching apparatus occurs when thecalling subscriber restores the receiver 2 to the switch-hook 3,

thereby breaking the connectionbetween the springs 6 and 8 at thesubstation, whereby the energizing circuits through the rotar linerelays 61, 81 and 109 of the switches are broken-that is, the lineconductors 27 and 28 are disconnected. The rotary line relay 109 of theconnector E, upon de-energization, permits the springs 149 and 150 todisengage, thereby breaking the circuit through the releasing relay 113.The releasing relay 113 in turn de-energizes and places in contact thesprings 151 and 152, thereby closing an energizing circuit through therelease magnet 120. This circuit extends from ground Gthrough thesprings 151 and 152, release magnet 120, normal springs 129 and 130 tothe batter lead 135, and through battery B to ground The release magnet120 being thus supplied with current energizes and operates in the wellknown manner to restore the connector shaft and shaft wipers to theirnormal position's; and when the normal arm 126 presses the springs 129and 130 out of contact the energizing circuit through the release magnet120 is broken. When the energizingcir-v cuit through the rotary linerelay 92 of the selector D is broken the springs 94 and 95 disengage,thereby breaking the energizing circuit through the release relayiw96.The release relay 96 of the selector D also deenergizes and places'thesprings 144 and and 102, release ma 145 in contact, whereby a circuit iscompleted through the release magnet 80 ofthe selector D. This circuitextends from ground G through the normal springs 101 et 80, releaserelay sprin s 145 and 144 to the battery lead 135, and tirough battery Bto ground G. The release magnet 80 in turn operates to release thesecond-selector D in the same manner in which the connector release maet operated to release the connector E. en the shaft 86 returns tonormal position, the normal armlOO carries the springs 101 and 1.02

out of engagement, whereby the circuit through the release magnet 80 is.broken, thus permitting the armature to return to normal position. In asimilar manner, when the rotary line relay 61 of the selector Cdeenergizes the sprin s 136 and 137 disengage,

thereby breaking t e circuit through the release relay 65. The releaserela selector C also (is-energizes an laces the springs 138 and 139 incontact, w ereby an energizing circuit is closed through the releasemagnet 66 of the selector C. This circuit extends from ground G" throughthe normal springs 74 and'73, release magnet 66, through the relaysprings 139 and 138 to the battery lead 135, and through battery B toground G. The release magnet 66 operates the same as the release magnet80 of the selector D to restore the first-selector shaft 34 and sideswitch to normal position. When the normal arm 70 permits the normalsprings 73, 74 and 71 to return to normal position the. energizingcircuit through the release magnet 66 is broken.

The busy-release of," the connector E follows as a result of thede-energization of the rotary line relay 109 if the called line is busy.4 If, when the private magnet 114 65 of the de-energizes for the lastdigit, the called line .subscriber (Fig. 1) presses the signaling button31 and energizes the vertical line relay 108, the latter then operatesthe vertical magnet 110. The vertical magnet in turn raises the switchshaft so that the normal post 126 permits the switch shaft sprin 127 toengage the contact point 128, and a usysignaling current is sent to thecalling subscribers station. The calling subscriber upon hearing thebusy-signal will under-' stand that the desired line is in service andwill release the switching apparatus over the been operated andestablished connection with the selector D,'and that it is desired torelease the selector C and make a new call. In that event, when thesubscriber restores the receiver 2 to the switch-hook 3 and separatesthe line conductors 27 and 28, the ener gizing circuit through therotary line relays 61 and 92 is broken, and in turn the energizingcircuit through the release relays 65 and 96 is broken. Similarly, theselector D and the connector E may be released before the switch hasbeen fully operatedthat is, during the operation of the switches inestablishing a connection, the central ofiice switches may, at theoption of the calling subscriber, be released and fully, restored.

The vertical and rotary line relays of the selector switches andconnector may be wound to any suitable resistance, but good results havebeen obtained when the coils were wound to a resistance of five hundredohms. While I have shown the vertical line relays as consisting ofheavier wire, therefore implying lower resistance, in order toillustrate the fact that they are not as sensitive as the rotary linerelays, it is to be understood that I do not wish to be limited to thisspecific construction, but may use any suitable means for obtaining suchoperation of these relays. The release relays 65, 96 and 113 may bewound to a resistance of one thousand ohms, and the substationresistance coil 29 to a resistance of three-thousand ohms.

From the foregoing it will be seen that I provide a full automatictrunking system inwhich automatic trunking is accomplished on apercentage basis, and without the necessity of employing operatinggrounds at the subscribers substations. Furthermore, it will be seenthat I provide means by which complete metallic line circuits areuniversally employed for controlling both the connecting and releasingoperations of any series of automatic switches which may be foundnecessary for extending connection to it called subscribers line. Thecalling subscriber can, of course, release at any time, either before orafter the called subscriber answers, and he thus has direct control overthe release at any stage of the call by the mere act of hanging up hisreceiver. In other words, the mere act of opening the calling telephoneline is sufiicient to release any switch or switches which may have beenbrought into service in extending connection to the called subscribersline. The retaining of a subscribers individual switch in an off-normalposition is absolutely contingent upon the closure of the line circuit,and if the line be not thus closed the individual switch thereof cannotremain in an off-normal position. In

this way the liability of constant trouble and annoyance from off-normalswitches is reduced considerably, and the work of supervising theexchange is materially simplified.

The transmitting of the call-signal" to thecalled subscriberis'initiated by simply shortcircuiting the calling telephone line, sothat no ground circuitsare employed outside of the exchange forsignaling purposes.

From what has already been said. will be seen that in the first selectorthe locking means for preventing the first selector G. from beingreleased comprises a slow-acting relay which is adapted to energize assoon as the line relay 61 is energized. This rela 61, it will be seen,is energized as soon as t e subscriber closes his line circuit, with theresult that the springs 136 and 137 are pressed into contact, therebvclosing the said circuit through the magnet 65. The magnet.. 65, uponenergizing, separates the springs" 138'and 139 in order to prevent therelease magnet 66 from energizing as soon as the switch shaft 70 israised from normal, at which time the s rings 74 and 7 3 come into.contact. The re ay 65 is made slow-acting so that it will not fall backwhen'the relay 61 de-energizes to permit the side switch to pass fromone position to another.. With this arrangement it will be seen that theswitch C is prevented from releasing until the line conductors 27 and 28are separated for a sufiicient length of time to enable the relay 65 tode-energize. As soon as the relay 65 de-ener'gizes, the energizingcircuit for the release magnet 66 is closed from ground Gr through thesprings 74 'and 73, through the said magnet 66 and through the springs139 and 138 to battery lead 135, and thence to battery. As soon as therelease magnet 66 energizes, the shaft is left free to return to normal.and as 'soon. as it reaches normal the energizing circuit for therelease magnet 66 is opened by that portion of the switch shaft marked70 which, it will be seen, is adapted to separate the-springs 73 and74;. With this arrangement it is obviousithat the switch is providedwith an automatic releasethat is, a release which follows automaticallyif the switch is ofi'normal and if the line circuit is open. The lockingmeans and automatic release at the selector D is exactly the same, themagnets'92, 96 and 80 corresponding to the magnets 61, 65 and 66. In theconnector switch a similar arrangement is employed, the magnets 109, 113and 120 being similar to the magnets 61, 6 5 and 66 of the selector 0. 7

What I claim as my invention is 1. An automatic telephone exchangesystalking circuit and the 2. A telephone exchange system comprising asecond-selector and a battery having one pole grounded, said selectorprovided with a vertical line relay permanently connected tonon-grounded battery, and with a rotary line relay permanently connectedto grounded "battery.

3. A telephone system comprising a battery having'one pole grounded, anda connector provided with a rotary line relay having one terminalthereof permanently connected to ground, and a vertical line relayhaving one terminal thereof, permanently connected to the non-groundedterminal of the battery.

4. A telephone system comprising a connector switch, a vertical relaypermanently connected between one side of the talking circuit and thenon-grounded terminal of a battery, and a rotary line relay permanentlyconnected between one side of the grounded terminal of the battery.

5. A telephone system comprising a second-selector switch provided witha rotary line relay bridged permanently between ground and themain-talking circuit,

and a side-switch operating magnet controlled by said relay,substantially as set forth.

6. A telephone system comprising a second-selector, and vertical androtary line relays for said selector, the vertical line relay beingbridged between the nongrounded terminal of a battery and one side ofthe main talking circuit and the rotary line relay being bridged betweenground and the other side of the main talking circuit.

7. An automatic telephone exchange system comprising a second-selectorhaving a side switch, said .selector provided with means having verticalmotion to select different operative levels depending on the numbercalled, and rotary motion to connect with a line in the selected level,and a rotary line relay having one terminal thereof permanentlyconnected to ground and the other to movable arm of the side switch.

8. A telephone exchange system comprising a second-selector providedwith means having vertical motion to select different operative levelsdepending on the number called, and rotary motion to connect with a'linein the selected level, and a battery having one pole grounded, saidselector also provided with a vertical line relay permanently. connectedto non-grounded battery, and with a rotary line relay permanentlyconnected to grounded battery.

9. A telephone system comprising a bat tery having one pole grounded,and a connector provided with means having vertical motion to selectdifferent operative levels depending on the number called, and rotarymotion to connect with a line in'the selected level, and-provided alsowith a rotary linle relay'ha-ving one terminal thereof permanentlyconnected to ground, and a vertical line relay having one terminalthereof permanently connected to the nongrounded terminal of thebattery. I

-1 A telephone 1 exchange system comprising a switch shaft, a rotaryline relay,

a private magnet, an energizing circuit for said private magnetcontrolled by said switch shaft and rotary line relay, said shaftprovided with means by which it is raised and rotated, and meansoperated by the said shaft and relay for setting up the said circuitwhile the said rotary line relay is energized and the switch shaft outof normal vertical position but in normal rotary position, saidenergizing circuit when established adapted to be broken either by therotation of the shaft, by the de-energizing of the rotary line relay, orby both.

11. A telephone system comprising a second-selector, a side switch forsaidselector, a private magnet for controlling the side switch, a shaft,and a plurality of energizing circuits for the private magnet, one ofsaid circuits controlled by the switch shaft and the other controlled bythe side switch.'

112. A telephone system comprising a second-selector, a private magnetfor said selector, a switch shaft, a private wiper, a side switch, theprivate magnet adapted to control the side switch, and a plurality ofenergizing circuits for said private magnet, one of said circuitscontrolled by the switch shaft, and another of said circuits saidselector, a switch shaft, a private wiper, a side switch, the privatemagnet adapted'to control the side switch, and a plurality ofenergizingcircuits for the said private magnet, one of said, circuitscontrolled by the switch shaft, and another of said circuits controlledby the side switch and private wiper, substantially as set forth. 15. Atelephone system comprising a bridging first-selector, a private magneta private wiper, a

therein, a. switch shaft, side switch, the private magnet adapted tocontrol the side switch, and a plurality of energizing circuits for thesaid private magnet, one of said circuits controlled by the switchshaft, and another of said circuits controlled by the private wiper,substantially as set forth.

16. A telephone system compr sing a se lector, a vertical line relaytherein brldged between one sideof the main talking line and thenon-grounded terminal of a battery, a rotary line relay bridged betweenthe grounded terminal of the battery and the other side of the maintalking line, and a bridge-cut-off relay adapted to disconnect the saidvertical and rotary relays from the 1 battery.

17. A telephone system comprising a selector, a line terminating in saidselector, a release magnet and a bridge-cut-ofl' relay in said selector,said relay having contacts for disconnecting both sides of said linefrom the battery, a switch shaft, and energizing circuits for saidrelease magnet and said bridge-cut-ofi' relay under the control of theswitch shaft, substantially as set forth.

18. An automatic telephone exchange system comprising a second-selectorprovided with a rotary line relay having a normally open energizingcircuit, means for extending connection to the said selector, and meansfor closing said circuit at the instant that connection is completed tothe said selector, said energizing circuit comprising the callingsubscribers' line conductors, a substation high resistance coil, and avertical line relay at the selector.

l9. A telephone system comprising a subscribers line, a subscribersstation, a switch allotted to said line, means at the substation forcontrolling said switch over a metallic line circuit, a plurality ofrelays in series with said line for operating said switch, one of saidrelays connected to the nongrounded pole of battery, and the otherconnected to ground, and a resistance-com trolling means at thesubstation for operat ing said line relays.

20. A telephone system-comprising a subscribers telephone, a line forsaid telephone comprising two parallel metallic conductors, a switch for.said line, line relays for operating said switch in series with theline, and means whereby one or both of said relays may be energized overthe two sides of the line in series.

21. A telephone system comprising a subscribers telephone line, a seriesof automatic switches, and means whereby the said switches are operated.to select other lines by varying the resistance of the line and bybreaking the line.

22. A telephone system comprising a subscribers telephone, a series ofautomatic switches, and means whereby the said switches are selectivelyoperated by varying the resistance of the line suddenly from a givennormal resistance to a lower resistance.

23. In a telephone system, the combination with a telephone circuitextending between distant stations, ofan automatic selector switch atone of said stations and a sending device at the other of said stationsadapted to control said switch over said circuit, said sending devicecomprising a resistance included in said circuit when the device is innormal position, and means governed'by said sending device in the op-.eration thereof for intermittently short circuiting said resistance.

24. In a telephone system, the combination with a telephone circuitextending between distant stations. of an automatic selector switch atone of said stations and a sending device at the other of said stationsadapted to control said switch over said cir-- cuit, said sending devicecomprising a re sistance included in said circuit, and a switchindependent of said sending device for intermittently short-circuitingsaid resistance. 1

25. In a telephone system, the combination with a telephone circuit, anautomatic selector switch controlled over said circuit and a sendingdevice for controlling said switch, said device comprising a resistancebridged across said circuit, and means independent of said sendingdevice for intermittently short-circuiting said resistance.

26. In a telephone system, an automatic directively controlled selectingswitch for use in connecting calling and called lines, a control circuitfor said switch, a device for varying the resistance of said circuitbetween fixed limits to produce a series of current impulses in saidcircuit, and operating mechanism for said switch non-responsive to theclosure of said circuit but responsive'to said impulses to advance saidswitch a variable amount depending on the number of impulses received.

27. In a telephone system, an automatic directively controlled selectingswitch for use in connecting calling and called lines, a control circuitfor said switch including the station on a calling line and two metallicconductors each extending from said station to said switch, said circuithaving two different resistance values, a device for rapidly andintermittently changing the resistance from one value to the other aplurality of times, and step by step operat ing mechanism for saidswitch responsive to the resulting current changes in said circuit. i

28. In a telephone system, an automatic directively controlled selectingswitch for use in connecting a calling and a called line, a controlcircuit for said switch established by the calling subscriber, saidcircuit having two different resistance values, a calling device at thestation on the calling line operable to change the control circuitresistarice a plurality of times in accordance with a digit in thecalled number, thereby producing alike plurality of substantially equalmomentary current impulses in said circuit and operating mechanism insaid switch responsive to the said impulses.

29. ,In a telephone system,'a subscribers line comprising two metallicconductors extending from the substation to the exchange, a series ofautomatic switches, means at the station on said line for closing aswitch control circuit including said two conductors, means for thenoperating said switches successively by intermittently varying thenormal resistance of said circuit, and means in each switch except thelast effective after the switch is operated for transferring the controlcircuit to the next switch in the series.

30. In a telephone system, a calling subscribers line, a series ofautomatic switches, a calling device at the station on the calling lineoperable after the receiver is removed to lower the normal resistance ofthe line a pluralityof times and then increase the same, and means foroperating said switches responsive to resistance variations to connectsaid line with a called line.

31. In a telephone system, a calling subscribers line, an automaticswitch for connecting said line with a called line, a calling device atthe station on said line comprising a resistance normally included inthe line circuit when the same is closed, said device also includingmeans for producing directive series of impulses by cutting saidresistance out of the line circuit a plurality of times, and operatingmeans for said switch responsive to said impulses.

32. In a telephone system, a subscribers line, an automatic switch, acontrol circuit for said switch established when the receiver is removedat the station on said line, said.

switch being irresponsi ve to normal current in said circuit, and acalling device at the said station for intermittently decreasing theresistance of said circuit in accordance with a digit in a called numberto operate said switch.

33. In a telephone system, a calling subscribers line, an automaticdirectively controlled switch, a closed control circuit for said switchincluding the said subscribers line, a calling device at the station onsaid line for producing a variable series of impulses in said circuit bydecreasing the'normal resistance thereof a variable number of times, andrelay mechanism in said switch for controlling its operation inaccordance with the series of impulses produced.

34. In a telephone system, a calling sub- 'scribers line, an automaticdirectively controlled step bystep switch, a closed con trol circuit forsaid switch including said subscribers line, a calling device at the Station on said line for producing: impulses of increased current insaid'circuit, and a step: ping relay in said switchirresponsive tonormal current in said circuit but responsive to said increased currentimpulses to operate said switch.

35. In a telephone'system, an automatic directively controlled switch, aclosed control circuit for said switch including a source of current, acalling device for producing a variable series of increased currentimpulses in said circuit, and a relay in said switch irresponsive tonormal current in said circuit but responsive to said increased currentimpulses to operate .said switch to an extent determined by the numberof impulses received.

36. In a telephone system, an automatic switch having directive primaryand automatic secondary movements, a closed control circuit for saidswitch, means for intermittently changing the resistance of saidcircuit, means for opening the circuit, means for operating said switchin its primary movement responsive to the resistance changes, and meansfor accomplishing'the change over from primary to secondary movementresponsive to the opening of the circuit.

37. In a telephone system, an automatic switch having directive primaryand second ary movements, a closed control circuit for said switch,means for intermittently altering the resistance of said circuit toproduce variable series of impulses therein, means for opening the saidcircuit, means for operating said switch in its two movements responsiveto two series of said impulses, and

means for accomplishing the change over from primary to secondarymovement responsive to the opening of the said circuit.

38. In a telephone system, an automatic switch having directive primaryand second ary movements for selecting a called line, a closed controlcircuit for-said switch, means for intermittently altering theresistance of said circuit to produce variableseries of impulsestherein, means for opening the said circuit, means for operatin saidswitch in its two movements responsive to two series of said impulses,means for accomplishing the change over from primary to secondarymovement responsive to the opening of the said circuit, and means forcompleting the connection to the. called line responsive. to anotheropening of the said circuit.

39. In a telephone system. the combination with a series of variablyadjustable switching devices, of a circuit for controlling said devices,means for producing resistance changes in said circuit and means for oening the same, means for adjusting said c evices responsive toresistance changes in the circuit, and means for switching said circuitto successive devices responsive to the opening of the circuit.

40. In a telephone system, the combination with two variably adjustableswitching devices, of a control circuit including a resistance, meansfor closing a shunt around said resistance, means for opening saidcircuit, and two relays included in said circuit, one of saidrelaysbeing responsive each time the said shunt is closed to adjust thefirst of said devices, and the other relay being responsive when thecircuit is opened to switch the circuit into association with the secondof said devices.

41. In a telephone system, an automatic directively controlled selectingswitch for use in connecting calling and called lines, a control circuitfor said switch including two metallic conductors ea'ch extending fromthe station on a calling line to said switch, said circuit having twodifferent resistance values, a device for changing the resistance fromone value to the other a plurality of times, operating mechanism forsaid switch responsive to the resulting current changes in said circuit,means for changing the control circuit resistance to a still differentvalue by opening the circuit, and releasing mechanism for said switchresponsive when the circuit is opened.

42. In a telephone system, a subscribers line, a series of automaticswitches, means at the station on said line for closing a switch controlcircuit, means for then operating said switches by intermittentlydecreasing the normal resistance of said circuit, means for opening saidcontrol circuit after the switches have been operated, and releasingmechanism for said switches responsive when the control circuit isopened.

43. In a telephone system, a calling subscribers line, an automaticswitch for connecting said line with a called line, a calling device atthe station on said line comprising a resistance normally included inthe line circuit when the same is closed, said calling device alsoincluding means for producing directive series of impulses by cuttingsaid resistance out of the line circuit a plurality of times, operatingmeans for said switch responsive to said impulses, means for opening theline circuit after the said switch has been operated, and releasingmechanism in said switch responsive when the line circuit is opened.

44. In a telephone system, an automatic directively controlled switch, aclosed control circuit for said switch including a source of current, acalling device for producing a. variable series of increased currentimpulses in said circuit, a relay in said switch irresponsive to normalcurrent in said circuit the substation,

a second relay in said switch responsive to normal current in saidcircuit but irresponsiye to impulses therein for preventing the releaseof said switch while the same is in use.

45. In a telephone system, a subscribers line, an automatic directivelymovable switch for connecting Said line with a called line, two linerelays for controlling the operation and release of said switch, one ofsaid relays being a marginal relay and the other a nonmarginal relay, acontrol circuit including said line and the two relays in series, and aresistance at the stat-ion on said line for controlling the marginalrelay.

46. In a telephone system, an automatic switch having a motor magnet anda release magnet, a control circuit for said switch, two relays and abattery included in said circuit in series, means controlled by onerelay for actuating said motor magnet, and means controlled by the otherrelay for actuating said release magnet. I

47..In a telephone system, a subscribers line, an automatic directivelymovable switch for connecting said line with a called line, a controlcircuit for said switch, means at the station on said line for closingsaid circuit and for then transmitting impulses over said circuit, arelay in said circuit non-responsive to the closure of said circuit butresponsive to said increased current imto said impulses to control theoperation of said switch, a second relay in said circuit irresponsive tosaid impulses, and release mechanism said second relay.

48. In a telephone system, an automatic directively movable switch foruse in connecting a calling and called line, a control circuit for saidswitch, means for producing a series of impulses in said circuit, arelay in said circuit responsive to impulses to control the operation ofsaid switch, another relay in said circuit irresponsive to saidimpulses. a slow acting relay controlled by said second relay, and arelease magnet for said switch controlled by said slow acting relay.

49. In a telephone system, atwo-conductor subscribers line insulatedfrom ground at an automatic directively controllable switch, a linerelay in said switch energized over the two sides of said line inseries, means for controlling the operation of said switch over thesubscribers line while maintaining said relay energized, and a releasemagnet in said switch controlled by said relay.

50. In a telephone system, a subscribers line. an automatic directivelycontrollable switch, a line relay in said switch energized over the twosides of said line in series, means for said switch controlled by forcontrolling'the operation of said switch over the subscribers line whilemaintaining said relay energized, releasing mechanism for said switch,and a slow acting relay controlled by said line relay for controllingsaid release mechanism.

51. In a. telephone system, a subscribers line, an automatic directivelycontrollable switch, a line relay in said switch energized over the twosides of said line. in series, means for controlling the operation ofsaid switch over the subscribers line while maintaining said relayenergized,means for opening the line to deenergize said relay, a releasemagnet, and means for energizing said release magnet a definite timeinterval after said relay has fallen back.

52. In a telephone system, an automatic switch having primary andsecondary movement for connecting subscribers lines, a closed controlcircuit for said switch, means for operating said switch over saidcircuit without interrupting the same, means for producing long andshort interruptions in said circuit, means in said switch foraccomplishing the change over from primary to secondary movementresponsive to a short interruption in said circuit, and means forreleasing said switch responsive to a long interruption in said circuit.

53. la a telephone system, an automatic switch having primary andsecondary movement for connecting subscribers lines, a closed controlcircuit for said switch, means for producing resistance changes in saidcircuit to operate said switch in its primary movement, means forproducing long and short interruptions in said circuit, means in saidswitch for accomplishing the change over from primary to secondarymovement responsive to a short interrupt-ion in said circuit,-and meansfor releasing said switch responsive to a long interruption in saidcircuit.

54. In a telephone system, a series of auto matic directively controlledswitches for connecting a calling and a called line, a relay in eachswitch maintained energized throughout the duration of the connection toprevent its associated switch from releasing, parallel energizingcircuits for said relays grounded only at the exchange and eachincluding the two sides of the calling line in series, and releasemechanism in each switch responsive whenever the associated relay isdeenergized.

55. In a telephone system, a series of automatic directively controlledswitches for establishing a two conductor metallic talking circuit, arelay in each switch maintained energized after thetalking circuit isestablished to prevent the release of its associated switch, anenergizing circuit for each relay including. a portion of the talkingcircuit, and release mechanism in each switch contfolled solely by theassociated relay and independent of the relays in any of the otherswitches.

slow acting relay controlling the release of said switch, another relaycontrolling the change over from primary to secondary movement, and acircuit for energizing said relays in parallel.

57. In a telephone system, an automatic switch having directive primaryand auto matic secondary movements, a line relay for controlling saidswitch, a slow acting relay controlling the' release of said switch, aquick acting relay controlling the changeover from primary to secondarymovement, and a circuit controlled by said line relay including saidquick and slow relays in parallel. 7

58. In a telephone system, a calling subscribers line, a connectorswitch, a line relay in said switch energized over the two'sides of saidline in series, means 'for operating said switch over the calling lineto connect with a called line while maintaining said relay energized, asecond relay energized by said first relay, a test wiper, means fordeenergizing said relays after the called line is connected with, arelease magnet, and a circuit for said release magnet closed in case thecalled line is busy, said circuit including said wiper and contacts ofthe said second relay.

59. In a telephone system, an automatic connector switch, means forcontrolling the said switch over the'two sides of a calling line inseries to connect with and signal a called line, and means whereby thecalling subscriber can control the duration of the signalling operationwhile maintaining'the connection established.

6O.v In a telephone system, an automatic connector switch, means forcontrolling the said switch over the two sides of a calling line inseries to connect with and signal acalled line, a ringing relayforetiecting the signalling operation by projecting ringing current outover the called line, and subscriber operated means at the station onthecalling line for controlling said relay while the connection ismaintained.

61. In a telephone system, an automatic nector including the two sidesof the calling line in series, a resistance associated with saidcircuit, a push button operable by the calling subscriber to determinewhethersaid resistance is included in said circuit or not, and a ringingrelay in said connector re sponsive when the said push button is actuated to signal the called subscriber.

63. In a telephone system, a subscribers line, an automatic step by steprotary trunking switch individual to said line, two controlling linerelays for said switch normally connected to opposite poles of theexchange battery, a circuit for energizing said relays over the twosides of said line in series when the subscriber makes a call, and acut-oil? relay for disconnecting said relays from the battery when theline is called.

64. In a telephone system, a subscribers line, an automatic step by steprotary trunking switch individual to said line, two controlling linerelays for said switch, a circuit for said relays including the tworelays in series and the two sides of said line in series, and means atthe station on said line for energizing both of said relays or only oneof said relays over said circuit at the option of the subscriber.

($5. In a telephone system, a subscribers line, an automatic step bystep rotary trunking switch individual to said line, two controllingline relays for said switch, a circuit for said relays including the tworelays in series and the two sides of said line in series, means at thestation on said line for energizing both of said relays or only one ofsaid relays over said circuit at the option of the subscriber, anda-cut-ofi relay for disconnecting 'said relays when the line is called.

66. In a telephone system, an automatic switch having primary andsecondary movement, a switch control circuit, means vfor controlling theoperation and release of said switch over said circuit, and relaymechanism operated through contact springs closed by the switch shaft atthe beginning of the primary movement of said switch to permit theinitiation of the secondary movement after the primary movement iscompleted.-

67. In a telephone system, an automatic switch having primary andsecondary movement, a control circuit for said switch includ-- ing thetwo sides of a subscribers line in series, a line relay in said circuitand controlled thereover ,for controlling the primary movement, anotherrelay for controlling the secondary movement, oil normal springs closedat the beginning of'the primary movement, and a circuit for said secondrelay including said off normal springs. Signed by meat Chicago, CookCounty, Illinois, this 12th day of April, 1907.

EDWARD A. MELLINGER. lVitnesses EDWARD D. FALES, ARTHUR B. SPERRY.

